In apparatus of this kind, the vertical position of a body suspended in a tube section is substantially proportional to the flow of the fluid medium flowing through the tube section but dependent on the shape and dimensions of the tube section and suspended body, the nature of the medium and the operating conditions. A signal which indicates the vertical position of the suspended body is therefore usually not linearly dependent on the vertical position of the suspended body.
This non-linearity is of particular disadvantage in apparatus of this kind in which the length of tubing is opaque, e.g. made of metal.
Frequently, data transducers connected downstream or other secondary apparatus also operate in a linear manner. If the signals conveyed to them are not linearly dependent on the vertical position of the suspended body, the signals which they emit are not linear either. Any associated displays must therefore have non-linear scales or the like, which is extremely awkward from the manufacturer's point of view. This also applies when non-linear mechanical couplings are provided in order to make a display linear.